slower zoom?

Howdy,

I'm building a Storymap  tour of a 28,000 pixel wide medieval French map (http://tinyurl.com/mdxuktg).  It's working  pretty well, however it zooms in so fast you don't really get to see the fly-in.  

Is there a way to slow down the zoom-in speed?

Thanks for a cool product,

Andrew Taylor, [e-mail]